When we presented the new René Herse cranks last week, a number of people wondered whether they would be strong enough. After all, most cranks have four or five spider arms, whereas the Herse cranks use only three. And what about the small bolt-circle diameter? Does it support the chainrings sufficiently?

Classic components have one major advantage: They have proven themselves. We don’t have to guess whether they are a good design, we can look at their record. Or records – because numerous performance records have been set with René Herse cranks.

The photo above is from the Summer 2011 Bicycle Quarterly. It shows Lucien Détée and Gilbert Bulté on their way to a record in the Journée Vélocio hillclimb. That climb was about 3 km (2 miles) long, up a steep hill near Paris that maxed out at 15%.

Their Herse tandem is equipped with Herse cranks. Think of the forces on that large 54-tooth chainring as this powerful team sprints out of the saddle, up this steep hill, in an all-out effort.

Détée and Bulté were among the strongest randonneurs of their era. They just had been the fastest riders in the 1956 Paris-Brest-Paris. They also set a record in the 100 km (64 mile) time trial, averaging over 43 km/h (27 mph). All these rides, and many more, were on René Herse cranks. I asked them whether they ever had problems with their cranks or chainrings, and the answer was: “No.” If Herse cranks were stiff enough for the combined forces of these two riders, they will be fine even for the most powerful racers.

Speaking of powerful racers, here is Geneviève Gambillon on the way to winning the 1972 world championships, on a René Herse bike with Herse cranks. She was known for her powerful sprint, and she used it to devastating effect at the world championships. She repeated her performance two years later, winning the 1974 world championships in Montreal. (The photo is taken from our book The Competition Bicycle.)

René Herse cranks has proven themselves over decades and millions of kilometers of hard riding. We are confident that the new production will be at least as reliable.

So why do other makers use more arms on their spiders and larger bolt circles? That is a topic for a separate post: stay tuned.

27 Responses to René Herse Cranks – Strong Enough?

Scroll down to the previous post, and you see two views (side and head-on) of the new 2011 René Herse crank. That is a final forging, not a CNC-machined prototype, so the production cranks will be exactly the same.

The 70 mm bolt circle is much older than the 86 mm FSA bolt circle. We wanted the cranks to be backwards-compatible, because many owners of René Herse bikes need chainrings. Furthermore, using a proven design has the advantage that we know it works well. If we adapted the design to a different bolt-circle, we’d have to change many things, and no longer could infer the reliability from past performance.

Jan,
Could you mention, in your upcoming post, something about the strength differences between a hot forged and cold forged part? My knowledge of metallurgy verges on nil; is stress corrosion something that can be prevented by owner maintenance, i.e., polishing, or is it a deeper process?

Second, somewhat off topic, my TA left crankarm broke at the spindle hole after five years of service from new. I was able to pick up a used, corroded TA crankset, upon starting to polish the left crankarm, lo!, what do I see but a crack forming in exactly the same place. Thoughts? I had always used a generally recommended torque setting of 350 in/lbs. Too much, or is something else at play?

I have used TA cranks on numerous bikes, for many years, without problems. All of my TA cranks came to me used, with many miles. They have been installed and taken off numerous times.

It seems to me that the problem you describe could be caused by overtightening – usually not during the initial installation, but when checking and re-tightening crank bolts. I don’t use a torque wrench, going by feel, but 40 Nm (350 in-lb) seems like a lot of torque. Can you even put that much torque on the crank bolt with a standard crank bolt wrench?

Oh yes, 350 in/lbs of torque is easy obtained. I use a Park Tools wrench and they quote a range for the crankarm bolt of 250 to 350 in/lb on their chart; perhaps I’ll go with the lower end. One of the reasons I got a torque wrench is I tend to follow the thought that if enough is good enough, a bit more is better!

May I (very kindly) express my surprise that you go by feel!? I’ll have to put you on a slightly shorter pedestal!

Feel and experience have served me well. The last time I broke a bolt was in 1989, when I tightened the stem bolt on my first racing bike. The bolt must not have been greased well, or it was faulty. It snapped… I also don’t use a tensiometer when building wheels, yet my wheels stay true, even when they are 8-speed rear wheels with non-offset rims.

The best mechanics I know, both in the bicycle and car world, never used a torque wrench. I have looked over René Herse’s tools, and there wasn’t a torque wrench in sight. I doubt Spence Wolf used a tensiometer when he built his famous wheels that stayed true for decades.

Of course, with that approach, it’s hard to communicate what is tight enough and what is too tight. A torque number allows inexperienced mechanics to replicate the values of experienced ones. But if the number is wrong, then there is trouble. The fact that your TA crankarm broke, in a way that rarely happens, indicates the the number you used was too high.

I have read elsewhere that re-tightening can be a problem as the torque is additive (to some degree). Perhaps on original installation the square taper is driven in a specific distance and re-tightening to full spec drives it further than needed? For less experienced mechanics that are not confident enough to work by feel (me included), is it best to pull the crank and then tighten the bolt to the spec, or perhaps just re-tighten to 50% or 75% of spec?

Yes, it appears to be a bad idea to tighten your crank bolts time and again. Basically, install them and leave them. Every couple of years, take off the crank entirely and re-install. Jobst Brandt has written about this topic in detail, and I think he is right on this one.

Nice post! Unstated but worth reinforcing is that the drive ring (front in this bike) is transferring the torque from both riders to the drivetrain. The arms on the front crank, however, are delivering the torque of only the front rider (the other is going to the crank through the timing chain). So the tandem is a nice test case for the 3-arm spider, but no better than a single bike for the arms.

I have no doubts about the arms, however. They look no thinner than those ridden by Coppi or Anquetil or Gaul. Photos of the relatively thin cranks ridden by these riders makes one think the modern obsession with crank arm thickness for anything shy of a world-class (or overweight) rider is unjustified,

The Herse crankarms (like Stronglight and TA) are more square in cross-section. So there isn’t much less material than in modern arms, but the Herse arms are a bit stronger in torsion (twisting). Cranks mostly are stressed in torsion, because the rider pushes on the pedal, which is offset to the outside of the crankarm. This puts a twisting motion on the arm. I haven’t analyzed other lightweight cranks, but I suspect that these are at least as strong as most.

On the other hand, chainrings and crank spiders are mostly stressed in the plane of the chainring, and thus don’t undergo huge stresses. Even the relatively thin modern TA chainrings work well, even though they have an even smaller bolt circle. We used one on the tandem in PBP 2003), and despite some considerable forces in training and during the ride itself, we had no problems. After more than 1000 miles, the ring remained true…

Historical performance does seem to indicate that the René Herse crank had evolved into a lightweight and robust design for racing, cyclotouring, and tandem use by the mid-1950’s. How many Herse cranks were extant over the original design run (say, 1950’s to 1970’s)?

Given that the new design uses a stronger forging alloy and is a minor modification to the later, 1970’s design, did the team model the new crank design to look for potential stress risers, weak points and to check it for fatigue resistance? How did the RH crank design team adjust the historical René Herse design, and were they able to model the crank’s performance given the improved material analysis tools available today?

The main advantage of the “long chain” or “front drive” tandem setup are shorter chainstays, because you don’t need to leave room for multiple chainrings behind the rear BB. Since tandems already are very long, builders tried to keep the wheelbase short to make the tandem handle better.

A minor point is that the front rider can operate the rod-operated front derailleur, but even back then, Herse offered cable-operated derailleurs, so this cannot have been the main reason.

The custom steel Moots mountain bike tandem which I used (with stoker Ed Levinson) to set the 24-Hour World Record for Tandem Mountain Biking back in 1990 had the triple crank up front. What I liked about it was that I could look down to see the interaction of the front derailleur and the rings. Also, it allowed my much shorter stoker to have a narrower Q-factor (tread). I was amazed that the long chain and its inherent extra flex didn’t shift poorly, but then again, the bike had a nice, fat chain with only seven cogs in back, so there was plenty of wiggle room. I wish I still had that bike!

I might be wrong, but I seem to remember reading an article somewhere where a rider talked of breaking rene herse cranks. It was either a contemporary interview of an older rene herse rider, or a translation from a vintage magazine. Could it have been in BQ?

If I remember right, it was a heavier sprinter, and thus probably not relevant for most of us.

That was Roger Baumann. He was the fastest single-bike rider in Paris-Brest-Paris 1956. Bicycle QuarterlyVol. 1, No. 2 had an interview with him, plus the story of that year’s PBP. He broke all kinds of aluminum cranks: Stronglight, Herse and TA. Nobody could figure out why he broke them. Sure, he was strong, but not that much stronger than the other riders. For PBP, he rode with steel Stronglight cranks with a square taper. Those are pretty massive, and they held up fine. It seems that in recent years, Monsieur Baumann’s pedal stroke has changed, because he now rides aluminum cranks with no problems. He co-holds the record for the most PBP finishes. He has ridden 10, the last in the 1990s. He still rides thousands of kilometers every year.

That is one of two reports of broken Herse cranks I have heard. The other was a vintage bike in Australia, I believe, where the crank broke after many decades. With more than 6000 Herse bikes made, most of which were equipped with Herse cranks, and many of which were ridden very hard, that does not appear to be a high failure rate. Still, any crank can break, and if you are like Monsieur Baumann and break cranks right and left, I would not recommend these.

There was a cyclist named Gary Verrill who raced the Race Across America in 1986 in 10 days, 5 hours as a rookie entrant. In 1987 we trained together quite a bit, but unfortunately he couldn’t compete in ’87 because he was hit by a motorist not long before the race. Gary was somewhat large and muscular (perhaps 6′ and 190 lbs) and rode out of the saddle a lot; he reminded many of us of Lon Haldeman. Gary broke cranks regularly: Campy, Galli, and all other other brands. They broke in all possible places: at the pedal hole, near the spider, even mid-arm. It always happened when he was standing on the pedals, usually in rolling terrain. Every time he broke a crank, he would, of course, crash, because of the suddenness of the incident. He was a great rider and a super nice guy, and there was nothing unusual about his riding technique or equipment set-up or choices. He just simply broke cranks. We all thought it was pretty cool, actually!

Jan did you do any deflection tests with a typical ring configuration to see how it compared to modern cranks with more arms and larger BCD’s (but thinner rings and maybe other compromises for weight/cost reasons)?

We haven’t tested chainring deflection, because it’s not an issue. I don’t think Campagnolo and Shimano give values for that, either. Even TA chainrings are fine when used by strong tandem teams, without the chain rubbing on the front derailleur even under very hard efforts while cross-chaining (big-big combination). This indicates that chainring deflection must be very small. Of all the concerns I have with cranks, this one is very low on the list.

The chainrings aren’t finalized, so we can’t give you an accurate weight yet. The arms weigh the same as the originals…

In production and shipping, there always can be delays, so we cannot tell you exactly when the cranks will arrive. That is also why we didn’t announce the cranks earlier. We wanted to make sure that production was imminent and that the cranks had passed the relevant EN tests.

Jan, thanks for your thoughts about torque: I agree with your observations. Upon reflection, the range Park gives, from 250 to 350 in/lb, seems quite a span! I’ll stick with the lower end in the future.
As always, food for thought, Now I’m pondering the mysteries of Mr.Baumann’s pedal stroke and crank breakage…

Hi Jan:
Just by way of explanation for for initial post. Like you, I am a firm believer in the frame designs that came out of France following WW 2, especially the tandem geometries (and 650 b wheels) that seemed to work so well.
A few years ago some good friends wanted a custom tandem, so Patrick did his research and approached a number of well known tandem builders about using randonneuring geometry and front drive. He was basically told – no, that won’t work, this is what you want. He related to me that front drive was a major sticking point for virtually all the people he spoke to.
He eventually found a builder in Philly who not only built what he wanted, but was so impressed with the ideas that my friend presented, he has built a few more frames using essentially the same design.

Tandems were much bigger in 1940s Paris than they are today. There were many very fast tandem teams who competed in various events. Even the mixed teams rarely consisted of husband and wife, but usually selected based on matching pedal strokes. For example, Monsieur and Madame Porthault both rode in the very first Flèche Vélocio. Madame Porthault rode the tandem with Jean Dejeans, and Monsieur Porthault rode a single. The PBP tandem records (both mixed and male) set in 1951 stood for 48 years!

This type of activity really focused the tandem builders on performance. Perhaps coincidentally, the low-trail geometries that were popular for 650B randonneur bikes were easily adapted for tandems… whereas the rear-loading “sport-touring” geometries popular in recent decades are ill-suited for tandems.

Re modern cranks using 4 or 5 spiders and larger bolt circles……I would guess that that may have been a response to the relatively low quality 3 spider cranks that were ubiquitous a few decades ago. If memory serves, I had a Nervex 3 spider crank on a vintage Raleigh on which the crank bolts had a real tendency to loosen, whereas for me, that has never happened on a 4 or 5 spider crank.